Microfluidic devices and systems have been gaining substantial interest as they are increasingly being demonstrated to be robust, highly accurate, high throughput and low cost methods of performing previously cumbersome and or expensive analytical operations.
In particular, microfluidic systems have been described for use in ultra high throughput screening assay systems, e.g., for pharmaceutical discovery, diagnostics and the like. See PCT Publication No. WO 98/00231, published Jan. 8, 1998. In addition, such microfluidic systems have reportedly been used in performing separations-based analyses, e.g., nucleic acid separations, etc. See, e.g., Woolley et al., Proc. Nat""l Acad. Sci., USA 91:11348-11352 (1994).
Despite the promise of microfluidic systems in terms of throughput, automatability and cost, many of the systems that have been described suffer from substantial drawbacks. Initially, many of these systems have substantial reductions in resolution over their counterpart methods on the bench top. In particular, a number of relatively minor considerations can readily become major factors when considered in the context of the relatively small amounts of material transported through these systems. For example, in microfluidic channels that include curves or turns, variations in distances through these turns and curves at the inside and outside edges can substantially affect the resolution of materials transported through these channels.
Further, simple operations, such as dilution and mixing have generally been accomplished at the expense of overall device volume, e.g., adding to the reagent/material volume required for carrying out the overall function of the device. In particular, such mixing typically requires much larger chambers or channels in order to provide adequate mixing of reagents or diluents within the confines of the microfluidic systems.
Thus, it would be generally desirable to provide microfluidic systems that are capable of capitalizing upon the myriad benefits described above, without sacrificing other attributes, such as resolution, volume, and the like. The present invention meets these and other needs.
The present invention generally provides microfluidic devices, systems and methods of using these devices and systems. The microfluidic devices and systems generally incorporate improved channel profiles that result in substantial benefits over previously described microfluidic systems.
For example, in one embodiment, the present invention provides microfluidic devices and systems incorporating them, which devices comprise a body structure and at least a first microscale channel disposed therein. The microscale channel typically comprises at least first and second ends and at least a portion of the microscale channel having an aspect ratio (width/depth) less than 1. In preferred aspects, the devices and systems include an electrical controller operably linked to the first and second ends of the microscale channel, for applying a voltage gradient between the first and second ends, and/or are fabricated from polymeric materials.
In a related but alternate embodiment, the present invention provides microfluidic devices and systems that comprise a body structure having at least a first microscale channel disposed therein, where the microscale channel has at least one turning portion incorporated therein. In this embodiment, the turning portion of the channel comprises a varied depth across its width, where the varied depth is shallower at an outside edge of the turning portion than at an inside edge of the turning portion. Preferably, the relative depths at the inside edge and outside edge of the turning portion of the channel are selected whereby the time required for a material traveling through the turning portion at the outside edge is substantially equivalent to a time required for the material to travel through the turning portion at the inside edge.
As alluded to above, the present invention also comprises microfluidic systems that include the above described microfluidic devices in combination with an electrical control system. The electrical control system is operably coupled to the first and second ends of the first and second channels, and capable of concomitantly delivering a voltage to each of the first and second ends of the first and second channels.